The invention pertains to a vacuum pump with a closable line through which gas ballast can be fed into the pump chamber of the pump.
In the case of vacuum pumps with an inner compression, there is the danger that sucked in vapours might condense in the pump chamber. No condensation will occur as long as the sucked in vapours are compressed by no more than their saturation vapour pressure. If, for example, water vapour is compressed to a higher pressure than this, the vapours condense in the pump and emulsify with the pump's oil. Thus the lubricating properties of the pump's oil reduce very rapidly so that there is the danger of rotor seizure. By admitting gas, preferably air--gas ballast--into the pump chamber of the pump, sucked in gases may be practically diluted thereby increasing the saturation vapour pressure, so that damaging condensations may not occur. It is known to equip the gas ballast facility with a manually operated valve, so that the gas ballast feed may be blocked off when it is not required.
From DE-A-702 480 vacuum pumps with gas ballast facilities are generally known. The rotary vane vacuum pump presented in drawing FIG. 1 of this document has a gas ballast facility where the quantity of the applied.sup.1) gas depends on the intake pressure. At a high intake pressure the valve is open; with reducing intake pressure the gas ballast feed is also reduced. In the case of a failure of a vacuum pump of this kind--for example, by a failure of the drive--the recipient is vented more or less rapidly via the gas ballast feed. FNT .sup.1) Translator's note: The German text reads . . . zugefuhrt . . . instead of . . . zugefuhrte . . . . The latter has been assumed for the translation.
It is known to prevent the recipient from being vented by means of an intake valve which is controlled according to the operating conditions. However, these solutions are involved and are out of the question for cheaper vacuum pump designs. A further possibility to prevent venting of the recipient, is, to ensure that the pump chamber of the pump is hermetically sealed in the case of a pump failure. A solution for this is known from the older application DE-A-42 08 194. In this solution, the oil supply to the pump chamber is blocked in the case of a pump failure, in order to avoid contaminating the recipient with oil vapours. However, functioning of this solution requires that a gas ballast facility not be present, or that it be closed manually prior to the pump failure. Known, so-called hermetically sealed vacuum pumps to date do not offer any protection of the vacuum with the gas ballast switched on.